Chemical manufacture



Patented Apr. 28, 1936 UNITED STATES 2,038,874 CHEMICAL MANUFACTURE Walter Lee Savell, Forest Hills, N. Y., The Mathieson Alkali Works, Inc.,

assignor to New York,

N. Y., a corporation of Virginia No Drawing. Application November 14, 1933, Serial No. 698,024

2 Claims.

This invention relates to improvements in the manufacture of viscose rayon.

In conventional practice the manufacture of viscose rayon proceeds about as follows: A highly purified cellulose, wood pulp or cotton linters, is saturated with an aqueous solution of caustic soda, containing 15%-20% NaOH by weight for example, and after separation of excess solution the saturated cellulose is held in appropriate containers for a period of hours to permit reaction between the cellulose and the absorbed caustic soda solution to proceed to the desired extent. After disintegration the product of this reaction is subjected to the action of carbon disulphide to form a cellulose derivative commonly designated sodium cellulose xanthate which is dissolved in a dilute aqueous solution of caustic soda. This solution is filtered and after appropriate aging, to effect the so-called ripening, becomes the spinning solution from which the yarn is formed. This spinning solution is forced through socalled spinnerets into an acid aqueous spinning bath and the yarn thus formed is collected on spools or in spinning pots. The cake of yarn from the spinning pot, or the spool of yarn, is washed and dried and reeled into skeins. The yarn as it leaves the spinning bath always contains some free sulphur and is normally discolored. As a consequence, conventional practice includes a desulphurizing operation and a bleaching operation as separate operations applied to the yarn after it leaves the spinning bath. The desulphurization is usually effected by subjecting the yarn to the action of an aqueous solution of ammonium sulphide or sodium sulphide. The bleaching operation is usually efiected by subjecting the yarn to the action of an aqueous solution of hydrogen peroxide or sodium hypochlorite.

The improvement of this invention, in one aspect the substitution of a novel step in this general procedure, makes it possible to combine such desulphurization and bleaching in a single operation in a particularly advantageous manner.

In accordance with this invention, the viscose rayon is subjected, as it leaves the spinning bath, to the action of an acid aqueous solution containing chlorous acid, HClOz. An appropriate solution can be formed by making acid, with sulphuric acid for example, an aqueous solution of sodium chlorite, NaClOz, containing for example grams NaClOz per liter. The concentration of the chlorite from which chlorous acid is formed in the solution is not important. It is essential, however, that the solution be acid. The degree of acidity, providing the solution has a pH not exceeding. about 6.5, is not important. This treatment of the yarn with an acid aqueous solution containing chlorous acid can be applied to the yarn at any time after it leaves the spinning bath to combine desulphurizing and bleaching;

In conventional practice the viscose solution always contains some sodium thiocarbonate,

formed as a consequence of reaction between sodium hydroxide and carbon disulphide necessarily present in excess of the amounts required to form the sodium cellulose xanthate, in order to have the reaction continue to the desired extent. In the acid aqueous spinning bath, this sodium thiocarbonate reacts to liberate carbon disulphide. In the manufacture of finer yarns this is not normally troublesome because it is liberated, substantially completel before the spun yarn is reeled into the form of skeins. In the manufacture of coarser yarns, however, such carbon disulphide is trapped within the spun yarn to an extent such that the yarn may still contain as much as 1% carbon disulphide by weight or more as it reaches the reeling operation. Carbon disulphide when present in such amounts occasions considerable distress and some poisoning of workers handling the yarn at this point in the general procedure. Steaming and washing, the conventional operations, have not proven completely adequate to cope wtih this difliculty when encountered.

Carbon disulphide, as well as free sulphur, is eliminated from the yarn by subjecting it to the action of an acid aqueous solution containing chlorous acid in accordance with this invention. Thus, by subjecting the yarn to the action of an acid aqueous solution containing chlorous acid after it leaves the spinning bath and before it reaches the reeling operation, the difliculties which would be encountered were carbon disulphide present in the yarn as it reaches the reeling operation can also be avoided.

I claim:

1. In the manufacture of viscose rayon the improvement which comprises removing carbon disulphide contained in the rayon by subjecting the rayon immediately after spinning to the action of an acid aqueous solution containing chlorous acid.

2. In the manufacture of viscose rayon the improvement which comprises removing carbon disulphide contained in the rayon by subjecting the rayon immediately after spinning and before reeling to the action of an acid aqueous solution containing chlorous acid.

WALTER LEE SAVELL. 

